Wafer Level Packaging (WLP) refers to the technology of packaging an integrated circuit (IC) at a wafer level, instead of the traditional process of assembling the package of each individual die on individual packages. One feature of the WLP is that the resulting integrated circuit package is practically the same size as the individual package diced. Furthermore, WLP provides a streamlining of the semiconductor manufacturing process from start to customer shipment.
Soldering structures are well-adopted in WLP for external electrical connections. These range from hand-soldering methods to machine soldering methods. It is well-known to use a flux material with the soldering material. The flux material satisfies a number of functions. Generally a main function of the flux material is to ensure that conductive material of a first component, for example a support substrate such as a printed circuit board (PCB) interconnects well with good electrical conduction across the solder interconnect to a second component such as an electronic component.
To form a successful interconnection it is often necessary to apply a flux material. A number of different alternatives have been used. It is known for example to include a solid flux material within the soldering material. Generally such a soldering material would then be provided in a wire or other such solid form which would incorporate a core of flux material running through the solder. As the solder melts upon heating, the flux is activated, and the resulting interconnect formed if the soldering process is of an acceptable standard. It is also known to use solder paste materials. Solder pastes are generally homogenous, stable suspensions of solder particles in a flux medium material.
Reflow soldering is used in the automated manufacture of PCB's, wherein electronic components are surface mounted on PCB's to which a solder paste material has previously been applied by a method such as screen or stencil printing or dispensing. The PCB is then subjected to a sufficiently high temperature, to cause the solder to liquefy and to join the components in place on the PCB. The heat can be supplied by, for example, infrared, heated conveyor belt or convective means.